The following relates to the electrical power grid arts, electrical power grid frequency control arts, and related arts.
Electrical power grid management includes maintenance of the target electrical frequency, e.g. at 60 Hz (in North America) or 50 Hz (in Europe). Electrical power generators are designed to operate at (by way of illustrative example) 60 Hz at a given load. If the load increases, this creates counter-torque on the generators which slows the mechanical rotation and consequently lowers the electrical frequency. Conversely, if the load decreases, the counter-torque is reduced, the mechanical rotation speed increases and consequently the electrical frequency increases.
In practice, the electrical frequency is measured in real-time to generate an Automatic Generation Control (AGC) signal. Based on the AGC signal, ancillary generators (typically gas-fired for rapid response) are throttled up or down to maintain the target electrical frequency. Rather than ancillary generators, energy storage devices such as batteries or flywheels can be used to absorb or inject power to maintain frequency. The ancillary generators (and/or batteries, flywheels, et cetera) are property of the power company and/or property of curtailment service providers (CSPs). In the former case, construction and maintenance of these frequency control devices is a direct cost to the utility company or other grid operator. In the latter case, the grid operator typically contracts with the CSP to obtain access to the ancillary generator for a prescribed time interval. In either case, scheduling of sufficient ancillary generator capacity typically done ahead of time, while the actual frequency control is done using the ancillary generators based on the AGC signal, typically with a response time of minutes to tens of minutes for throttle-up or throttle-down of the ancillary generators.
The requirement to maintain sufficient ancillary generator capacity available for frequency control introduces substantial overhead cost and energy waste to the power grid. Overhead cost arises due to the need to construct and maintain the ancillary generators, and/or the cost of contracting with CSPs for access to these devices. These costs can be reduced by improved aggregate load prediction or modeling; however, the grid operator still must plan for unexpected load swings due to weather changes, social events, unexpected industrial loads, and so forth. Energy waste arises due to operational inefficiencies of the ancillary generators (or batteries, flywheels, et cetera).
One approach that has been contemplated to reduce the need for ancillary generators or the like is to construct loads to perform frequency response. Such “frequency response loads” are designed to detect the a.c. line frequency and to increase power usage (at least on average) when the frequency goes above the target frequency and to decrease power usage when the frequency goes below the target frequency. Frequency response loads can in principle improve frequency regulation, but the decentralized nature of this approach limits its usefulness. The grid operator does not control the frequency response loads, and so cannot rely upon these loads to maintain the target frequency. Accordingly, frequency control performed by the grid operator dominates, and the frequency response loads typically can, at most, provide secondary “fine tuning” of the electrical frequency. (Indeed, it is possible that a high density of frequency response loads may actually be detrimental, if the load modeling employed by the grid operator does not take these loads into account).
Another approach that has been contemplated to reduce the need for ancillary generators or the like is Direct Load Control (DLC). In this approach, the grid operator directly controls load operation. By utilizing loads that have an energy storage and/or time lag facet, DLC can in principle provide a mechanism for frequency control. For example, heating, ventilation, and air conditioning (HVAC) systems have high thermal capacity due to the thermal capacity of the heated air volume. Similarly, hot water tanks have thermal capacity in the form of the stored hot water. Using DLC, the grid operator can operate such loads in a manner that minimizes frequency fluctuations while still maintaining the desired room temperature, water temperature, or so forth.